1. Field of the Invention
The present invention generally relates to a measurement apparatus that includes a liquid crystal display unit, and in which the power consumption is limited. More specifically, the present invention relates to the power supply to the liquid crystal display unit. In addition, the present invention relates to a measurement apparatus that includes a liquid crystal display unit and a plurality of setting units each of which sets internal data. More specifically, the present invention relates to technology for diagnosing abnormalities in consumption current in the liquid crystal display unit.
Priority is claimed on Japanese Patent Application Nos. 2009-183243, filed Aug. 6, 2009 and 2009-188977, filed Aug. 18, 2009, the content of which are incorporated herein by reference.
2. Description of the Related Art
Flow meters are used as measurement apparatuses to measure flow rates inside pipe lines used to construct plant facilities. The flow meters incorporate as a display unit a liquid crystal display module, hereinafter referred to as an LCD module, in which a transparent conductive film formed, for example, from Indium Tin Oxide, hereinafter referred to as ITO, a liquid crystal panel formed by a large number of pixels, and drivers that selectively drive the pixels of the liquid crystal panel are integrated into a single unit.
FIG. 6 is a block diagram illustrating a configuration structure of a flow meter in accordance with the related art. The flow meter includes an analog signal input unit 1, an A/D converter 2, a CPU 3, a nonvolatile memory 4, an output unit 5, a display unit 6, an internal power supply unit 7, and an external power supply 8. In FIG. 6, an analog flow rate signal S output from a sensor, which is not illustrated in the figure, is input into the analog signal input unit 1 to be normalized. Then the analog flow rate signal S that is normalized is input into the A/D converter 2 to be converted into a digital flow rate signal. Then the digital flow rate signal that is converted in the A/D converter 2 is input into the CPU 3.
The CPU 3 executes predetermined calculation processing on the digital flow rate signal in accordance with the application in which the signal is to be used, such as whether it is for external output or for display, based on programs stored in the nonvolatile memory 4. The respective calculation results are output to the output unit 5 or display unit 6.
The internal power supply unit 7 supplies power that is required to drive the respective units such as the analog signal input unit 1, the A/D converter 2, the CPU 3, and the display unit 6.
The external power supply 8 is connected to the internal power supply unit 7 through a transmission line L1. The external power supply 8 is connected to the output unit 5 through a transmission line L2. The transmission line L2 includes an adjusting resistor R. The external power supply 8 supplies power such as, for example, 24V of DC voltage to the internal power supply unit 7 via the transmission line L1. The external power supply 8 receives from the output unit 5 via the transmission line L2 and the adjusting resistor R DC current signals of between 4 and 20 mA that are associated with measured flow rate values.
The flow meter includes an LCD module as the display unit 6. The ITO film included in the LCD module may become corroded by ions which adhere thereto from an anisotropic conductive film or from contamination or the like, or by water that is present around the flow meter installation location, or by voltage that is applied when the flow meter is being operated.
In particular, in an LCD module in a flow meter which is operating at a high-temperature high-humidity installation site, deterioration is generated in the insulation around the drivers in conjunction with the corrosion of the ITO film, which causes an increase in consumption current. Any increase in consumption current is undesirable as there is a possibility that this will have a deleterious effect on the operations of two-wire measuring instruments, as well as measuring instruments having strict consumption current limitations such as battery type and radio type measuring instruments.
Liquid crystal display units such as LCDs, and setting units such as infrared touch switches and the like that set data for internal parameters are included in a measurement apparatus such as a flow meter that is used in chemical plants and factories and the like.
FIG. 7 is a block diagram illustrating a configuration structure of a measurement apparatus 1 in accordance with the related art. The measurement apparatus 1 includes an internal power supply unit 11, an A/D converter 20, a CPU 30, an LCD 40, a first setting switch 50, a second setting switch 60, a nonvolatile memory 70, and an output unit 80. Output voltage from an external power supply or internal battery, neither of which is illustrated in the figure, is input into the internal power supply unit 7. The internal power supply unit 7 generates internal power supply voltage, and supplies the internal power supply voltage to the A/D converter 20, the CPU 30, the LCD 40 and the like.
Flow rate signals FLD (i.e., processing signals), which are analog signals, are input from a sensor, which is not illustrated in the figure, into the A/D converter 20. The A/D converter 20 converts the analog signals into digital signals and then outputs the digital signals.
The CPU 30 receives the digital signals from the A/D converter 20. Then the CPU 30 reads internal parameter data from the nonvolatile memory 70, and calculates a flow rate value (i.e., a processing value) using the internal parameter data.
The CPU 30 outputs current or voltage signals which are proportional to the flow rate value via an output unit 80, and sends a display control signal DCNT that includes display data such as the flow rate value to the LCD 40. The LCD 40 displays display data such as the flow rate value included in the received display control signal DCNT.
The CPU 30 is provided with a measurement value display mode which displays the flow rate value on the LCD 40, and with an internal data setting mode which sets internal parameter data.
When the CPU 30 has been changed to the internal data setting mode, a user alters the internal parameter data by pressing the first setting switch 50 and the second setting switch 60, which are formed by infrared touch switches or the like, while viewing the current internal parameter data displayed on the LCD 40.
More specifically, internal parameter data modification signals are sent from the first setting switch 50 and the second setting switch 60 to the CPU 30. The CPU 30 modifies the internal parameter data based on the internal parameter data modification signals. The internal parameter data that is modified is stored in the nonvolatile memory 70 and is displayed on the LCD 40. Note that the internal parameters include, for example, the meter factor, flow rate span, and the like that are used to determine the flow rate.
An LCD module may be used for the liquid crystal display unit. This LCD module includes an LCD driver and the LCD 40. The LCD driver converts the display control signal DCNT into a voltage that is capable of being displayed on a liquid crystal display and drives the LCD 40.
The LCD module includes the LCD driver that is packaged on top of a glass substrate, an anisotropic conductive film, hereinafter referred to as an ACF film, which covers the LCD driver, and an ITO film that is sandwiched between the glass substrate and the LCD driver.
In the LCD module, corrosion is generated in the ITO film by ions adhering thereto from the ACF film or from contamination or the like, by peripherally present moisture, and by the voltage that is applied to the LCD driver at startup. In an LCD module that operates in a high-temperature high-humidity environment, as time passes, the progression of corrosion in the ITO film causes the insulation to deteriorate and generates an increase in consumption current.
In a two-wire processing instrument in which there is a limit on the externally supplied current, if the overall internal circuitry does not operate at 4 mA or less, the internal power supply voltage is reduced and the instrument does not operate normally. Therefore, when an LCD module is used for the two-wire processing instrument, consumption current increases and the instrument does not operate normally.
In measurement apparatuses that operate using an internal battery, the life of the battery is shortened by an increase in consumption current.
Even in measurement apparatuses other than two-wire processing instruments or measurement apparatuses that operate using an internal battery, a considerable amount of heat is generated in the internal circuitry, in particular, in the internal power supply unit 11 by an increase in consumption current, so that the lifespan of the component being used is shortened.
If an LCD module is used, when consumption current increase abnormalities are diagnosed by the CPU 30, a configuration can be employed in which the signals used for the diagnosis are newly input into the CPU 30. In this case, it is necessary to allocate an additional input port to the CPU 30, so that unless there is a surplus of input ports, creating the above type of configuration is difficult.